Recently, attention has focused on the quadriceps in the
treatment of knee OA pain. The quadriceps mechanism is
of key importance for walking, standing, and using stairs,
and weakness in this muscle may cause impaired function.
In addition, quadriceps weakness is a primary risk
factor for progression of joint damage in knee OA and
knee pain [9,14]. Slemenda et al. [15] found that less
quadriceps strength predicted both radiographic and
symptomatic knee OA. The odds ratio for the presence of
OA per 10-lb-ft loss of strength was 0.8 for radiographic
OA and it was 7.1 for symptomatic OA, indicating that
persons with symptomatic OA had weaker quadriceps
than those with asymptomatic OA. Further, O'Reilly et al.
found that quadriceps weakness was strongly associated
with pain in 600 community-dwelling individuals ages
40–79 with knee OA [9]. Subjects with knee pain had less
voluntary quadriceps strength than those without pain (t
= 3.90, p < .01). Quadriceps strength (Odds ratio = 18.8
for muscle strength ≤ 10 kgF) and radiographic change
(Odds ratio = 4.1 for radiographic score ≥ 4) are thus independently
associated with knee pain.